want of time, you may be obliged sometimes to accept or form a
conclusion tentatively or provisionally. You may be able to draw
correct conclusions from stated {31} premises even though you do not
understand the terms of the premises. For instance, if I say,
"Selenium is a dyad element" and "A dyad element is one capable of
replacing two equivalents of hydrogen," I can correctly draw the
conclusion that, "Selenium is capable of replacing two equivalents of
hydrogen," but I cannot know that the conclusion is correct unless I
understand the meaning of the terms in the premises and so can be sure
of the correctness of those premises.

Every student should, therefore, in the writer's opinion, take a
systematic course in logic, or carefully study by himself such books as
Jevons' "Elementary Lessons in Logic" or John Stuart Mill's "Logic."[4]

(_b_) LEARN TO STATE A THING IN DIFFERENT WAYS OR FROM DIFFERENT POINTS
OF VIEW.--Almost anything may be looked at from different points of
view, or a truth stated in different ways, {32} and it may appear very
different from different viewpoints. A student should practise doing
this, first stating a principle perhaps from the mathematical point of
view, and then in simple untechnical language that can be understood by
one who is not a mathematician. The habit of stating even technical
matters in simple untechnical language should be practised continually.
As Bishop Berkeley urged, we should "think with the learned and speak
with the vulgar." If you clearly understand a proposition, you can
state it in clear and unambiguous language, though perhaps not in
Addisonian English. Students frequently say "I understand that, but I
cannot explain it." Such a student deceives himself: he does not
understand it. If he understands it thoroughly, he can explain it
clearly and without ambiguity, and so that others will understand him.
For this reason an acute observer can get the mental measure of a man
after a few minutes' conversation. Inaccurate or slipshod thinking
will surely show itself in speech.

(_c_) STATE A THING NOT ONLY POSITIVELY BUT NEGATIVELY.--That is to
say, state not only what it is, but what it is not, even if
incompletely. Perceive not only what it includes, but what it
excludes. When a result or a {33} principle is arrived at, it is
essential not only to see that it is true, but how far the _reverse_ is
_untrue_. The student does not really understand a thing